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EP3947597A1 - Procédé de production d'une écorce d'oxyde autour de nanocristaux - Google Patents

Procédé de production d'une écorce d'oxyde autour de nanocristaux

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Publication number
EP3947597A1
EP3947597A1 EP20716172.0A EP20716172A EP3947597A1 EP 3947597 A1 EP3947597 A1 EP 3947597A1 EP 20716172 A EP20716172 A EP 20716172A EP 3947597 A1 EP3947597 A1 EP 3947597A1
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European Patent Office
Prior art keywords
shell
metal
core
group
ncs
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20716172.0A
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German (de)
English (en)
Inventor
Anna LOIUDICE
Raffaella Buonsanti
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Ecole Polytechnique Federale de Lausanne EPFL
Original Assignee
Ecole Polytechnique Federale de Lausanne EPFL
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Publication of EP3947597A1 publication Critical patent/EP3947597A1/fr
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J13/0004—Preparation of sols
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    • C09K11/7715—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing cerium
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
    • C23C16/45525—Atomic layer deposition [ALD]
    • C23C16/45527—Atomic layer deposition [ALD] characterized by the ALD cycle, e.g. different flows or temperatures during half-reactions, unusual pulsing sequence, use of precursor mixtures or auxiliary reactants or activations
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    • C01P2004/00—Particle morphology
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    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

  • the present invention relates to a method for producing core-shell nanocrystals consisting of a metal-containing nanocrystal core and a shell layer comprising at least one metal oxide material having variable shell thicknesses, and use of the core-shell nanocrystals for different applications.
  • Metal oxide core-shell nanoparticles are pivotal for many areas of science, including medicine, biology, optics, electronics, energy storage and catalysis. Most oxide shells are prepared via hydrolysis/condensation reactions, with one representative example being the so-called Stober method where tetraethylortosilicate is used as the precursor for the growth of silica shells.
  • Stober method where tetraethylortosilicate is used as the precursor for the growth of silica shells.
  • the main drawbacks of the available wet-chemistry approaches are the encapsulation of multiple nanoparticles within the same shell, which results in micron-size powders as the final product, and the poor control over the shell thickness below 5 nm.
  • ALD atomic layer deposition
  • gas- phase ALD suffers from some limitations such as the difficult control over the amount of precursor, which is dictated by the pressure range covered in the reactor, and the loss of colloidal stability in the case of powder reactors.
  • gas-phase ALD requires rather expensive equipment, it needs high vacuum and it requires higher temperatures, it can be applied in thin film or powders, though the latter is rarer.
  • silica is the preferred oxide. It can be grown in solution and one of the most common approaches is the Stober method, based on hydrolysis/condensation reactions. This method is carried out in solution but it is difficult to utilize for other oxides such as alumina or titania. One reason why one might want a different oxide is for the tuning of the chemical properties (i.e. silica is not stable in basic environment, instead titania is).
  • colloidal ALD allows to overcome these issues, however its potential has been mostly limited to the synthesis of chalcogenide core-shell nanoparticles.
  • Pioneering work in the field has been carried out by Itthuria et al. (J. Am. Chem. Soc. 2012, 134) with other follow-ups reported in the literature.
  • the ALD process starts with the functionalization of the nanocrystalline core surface with inorganic ligands (e.g. S 2 , Se 2 , SmSe 4 , etc.) followed by the addition of the chalcogenide precursor.
  • An aspect of the present invention provides a colloidal atomic layer deposition (c- ALD) method for producing core-shell nanocrystals consisting of a metal-containing nanocrystal core and a shell layer comprising at least one metal oxide material, the method comprising
  • metal-containing nanocrystal cores selected from the group comprising semiconductors, metals, metal oxides or combinations thereof, wherein the semiconductors are selected from the group comprising CdSe, ZnSe, InP, ZmP2, InSe, C-dot, CsPbX 3 (wherein X is Br, I, or Cl), or combinations thereof, wherein the metals are selected from the group comprising Ag, Au, Pt, Pd, or combinations thereof and wherein the metal oxides are selected from the group comprising CeCk , ZnO, TiCk, SiCk, or combinations thereof,
  • the reaction mixture containing one or more highly reactive organometallic compounds to the reaction mixture, wherein the one or more highly reactive organometallic compounds are able to produce volatile secondary products during the reaction and are preferably selected from the group comprising trimethyl aluminum, dimethylzinc, tetrakis(dimethylamido)titanium(IV), trymethylindium, trymethylgallium or combinations thereof,
  • terminating ligands selected from the group comprising fatty acids, long chain amine and phosphine oxides, or combinations thereof, to the reaction mixture to stop the growth of the metal oxide shell, wherein preferably the fatty acids are selected from the group comprising oleic acid, myristic acid, stearic acid, or combinations thereof, and wherein preferably the long chain amine and phosphine oxides are selected from the group comprising dodecylamine, oleylamine, trioctylphosphine, trioctylphospineoxide, or combinations thereof.
  • Another aspect of the present invention provides a core-shell nanocrystal consisting of a metal- containing nanocrystal core and a shell layer comprising at least one metal oxide material, obtained by the colloidal atomic layer deposition (c-ALD) method of the invention.
  • c-ALD colloidal atomic layer deposition
  • Another aspect of the present invention provides a use of the core-shell nanocrystals of the invention as quantum dots or semiconductor nanocrystals.
  • QD-LED quantum dot light emitting diode
  • Another aspect of the present invention provides a photovoltaic device comprising the core shell nanocrystals of the invention.
  • Another aspect of the present invention provides a catalytic material comprising the core-shell nanocrystals of the invention.
  • Another aspect of the present invention provides a bio-material comprising the core-shell nanocrystals of the invention.
  • Figure 1 shows A) Schematic of the c-ALD synthesis and B) sketch of the obtained core-shell NCs.
  • Figure 2 shows sketch of the c-ALD synthesis set-up.
  • Figure 3 shows HAADF-STEM images and corresponding EDX coloured maps of A,B) Ce0 2 @A10 x and C,D) Ag@A10 x NCs; E) EDX maps of Ag@A10 x NCs obtained at different c-ALD cycles.
  • F,G,H HAAFD-STEM images of CsPbBr 3 @A10x NCs without any shell, with thin (8 cycles) and thick (17 cycles) A10 x shell respectively;
  • Figure 4 shows low magnification TEM images of Ce0 2 @A10 x and Ag@A10 x core-shell NCs.
  • Figure 5 shows EDX maps of the CsPbBr 3 @A10 x thick shell and CsPbl 3 @A10 x with respective spectra showing that the Br signal overlaps with Al. Despite Br and A1 peaks overlap, from the EDX maps the AlOx shell could be clearly revealed and a shell size thickness of around 5.5 nm could be measured.
  • Figure 6 shows A) FIR-STEM image of a single CsPbBr 3 @A10 x NC showing that the lattice parameters are retained after the c-ALD process; B) UV-Vis absorption and photoluminescence spectra of uncoated CsPbBr3 NCs (continuous line) and CsPbBr 3 @A10 x NCs (dot lines) (the spectra are offset for clarity).
  • Figure 7 shows time resolved photoluminescence decays of uncoated CsPbBr3 and CsPbBr 3 @A10 x thick shell with the corresponding fit (red lines). See Table 2 for fit parameters.
  • FIG 8 shows photos of the uncoated CsPbBr3 (left) and CsPbBr 3 @A10 x (right) solutions deposited on water showing that the A10 x shell confers stability against water.
  • Figure 9 shows normalized Quantum Yield (QY) for the CsPbBr3 and CsPbE NCs obtained by adding increasing amount of trimethylaluminium (TMA).
  • QY Quantum Yield
  • Figure 11 shows A) FTIR spectra of Ag-OLAC@A10 x and CsPbBr 3 @A10 x NCs.
  • the gray area evidences the features corresponding to the A10 x shell;
  • Figure 12 shows A) TEM images of the Ag NCs with different surface chemistry along with a representative sketch: Ag-OLAM (blue), Ag-OLAC (red) and Ag-AgO (black); B) FTIR spectra of the samples in A); C) TEM images of the obtained Ag-OLAM@A10 x (left) and Ag- AgO x @A10 x (right) NCs.
  • Figure 13 shows UV-Vis absorption spectra of Ag-OLAM and Ag-AgOx NCs.
  • the Ag plasmonic peak is slightly red-shifted proving the presence of a very thin AgO shell in Ag- AgOx NCs.
  • Figure 14 shows A) TEM images of Ag-OLAM@A10 x NCs; B) EDX maps of Ag- AgOx@A10 x NCs; C) representative EDX spectra acquired on Ag-OLAM@A10 x and Ag- AgOx@A10 x NCs area like the yellow areas in A and B.
  • Figure 15 shows Photo of the set-up used during in-situ XRD anion exchange experiments.
  • Figure 16 shows A) Schematics of the anion exchange reactions investigated during the in-situ X-ray diffraction experiments; B) XRD spectra of the as-synthesized CsPbX 3 NCs used in the synchrotron experiments together with the XRD spectra of the final products: CsPb(Bro . 5lo . 5)3 and CsPb(Bro.5Clo.5)3 NCs.
  • Figure 17 shows TEM images with size histogram of A) CsPbBr3, B) CsPbb, and C) CsPbCb used for the anion exchange experiments.
  • Figure 19 shows A) Time evolution of the lattice parameters for the CsPbBr3 NCs (Lp Br- component) with increasing shell thickness when reacting with CsPbB NCs, specifically: Br no shell/ I-no shell (black), Br-shelll/I-no shell (green), Br-shell2/I-no shell (red), and Br- shell2/I-shelll (blue); B) Time-dependent change of the Lp for the Br-shell2 in presence of uncoated CsPbCb NCs.
  • Figure 20 shows time evolution of the normalized lattice parameters (Lp) for the CsPbBr3 component with increasing shell thickness in presence of CsPbCb NCs, specifically: CsPbBr 3 /CsPbCb no shell (black), CsPbBr 3 shelll/CsPbCb no shell (green) and CsPbBr 3 shell2/CsPbCb no shell (red).
  • the Lp normalization was performed by fixing the Lp minimum at zero and the Lp maximum at 1 for all set of data.
  • Figure 21 shows in a,b) the TEM images of the as-synthesized CsPbBr3 NCs and CdSe NPLs used for the semiconductor-semiconductor distance-dependence study and (c) corresponding normalized UV-Vis absorption (scatter line) and photoluminescence (continuous line) spectra acquired in solution.
  • Figure 22 shows a) the TEM images of CsPbBr 3 @A10x NC donor (D) mixed with CdSe NPLs acceptor (A) at 50D:50A (left) and 75D:25A (right) ratios; b) PLE spectra (vertically offset for clarity) collected at 570 nm for films at various D:A for an AlOx shell of 3.6 nm thick.
  • the gray and purple curves are the PLE spectra for the A-only and D-only films.
  • the dashed lines indicate the position of the maximum for the donor (black dashed line) and acceptor (gray dashed lines).
  • Figure 23 shows a-b) time- and energy-resolved PL intensity maps for short distance (2.4 nm) and long distance (4.7 nm) in equimolar binary mixtures containing both spectral information and decay dynamics c) Spectra from early and late time windows 0-10 ns (solid line) and 80- 95 ns (dashed line) for the neat donor and acceptor (top) and for the 50% binary mixture at long and short distances.
  • Figure 24 shows a-b) the decay dynamics of the features centred at 510 nm and 544 nm respectively, comparing the decay dynamics of the neat donor and acceptor with the one in the binary mixture at short and long distances.
  • FIG 26 shows normalized QY for the CsPbBr3 NCs obtained by adding increasing amount of trimethylaluminium (TMA), dymethylzinc and tetrakis(dimethylamido)titianium (IV).
  • TMA trimethylaluminium
  • IV tetrakis(dimethylamido)titianium
  • Figure 27 shows TEM images and corresponding EDX maps of the a) CsPbBr3@TiO x and b) CsPbBr3@ZnO x NCs with a TiOx and ZnOx shells grown by using the c-ALD.
  • Figure 28 shows the TEM images and corresponding EDX map of the a) CdSe@A10 x and b) CdSe@ZnO x NCs with a AlOx and ZnOx shells grown by using the c-ALD.
  • Figure 29 shows TEM image and corresponding EDX map of the C-Dot@TiO x with an AlOx and ZnOx shells grown by using the c-ALD.
  • the terms“nanocrystal” and“nanoparticle” can be used interchangeably in embodiments of the invention.
  • the term“at least one metal material” intend to include “one metal material”, so that a shell layer comprises only layers of one and the same metal material, or more than one metal material (i.e. a plurality of different metal materials), so that a shell layer comprises a plurality of layers, wherein some layers comprise different metal material from the other layers, such as for example a shell layer may comprise one layer of AI2O3- X (where 0 ⁇ x ⁇ 3) and another layer of Ti0 2-x (where 0 ⁇ x ⁇ 2) and/or ZnOi- x (where 0 ⁇ x ⁇ l).
  • AI2O3- X (where 0 ⁇ x ⁇ 3), TiCk- x (where 0 ⁇ x ⁇ 2) and ZnOi- x (where 0 ⁇ x ⁇ l) are abbreviated as AlOx, TiOx and ZnOx.
  • a colloidal atomic layer deposition c-ALD
  • the c-ALD developed synthesis has the advantage of preserving the colloidal stability of the nanocystalline core while controlling the shell thickness from 1 nm to 20 nm, preferably 1 nm to 6 nm.
  • An aspect of the present invention provides a colloidal atomic layer deposition (c-ALD) method for producing core-shell nanocrystals consisting of a metal-containing nanocrystal core and a shell layer comprising at least one metal oxide material, the method comprising
  • metal-containing nanocrystal cores selected from the group comprising semiconductors, metals, metal oxides or combinations thereof,
  • the semiconductors are selected from the group comprising CdSe, ZnSe, InP, ZmP2, InSe, C-dot, CsPbX 3 (wherein X is Br, I, or Cl), or combinations thereof; preferably the semiconductors are selected from the group comprising CdSe, C-dot, CsPbX 3 (wherein X is Br, I, or Cl),
  • the metals are selected from the group comprising Ag, Au, Pt, Pd, or combinations thereof; preferably the metals are selected from the group comprising Ag, Au, Pt, Pd; more preferably the metal is Ag,
  • the metal oxides are selected from the group comprising CeCk , ZnO, TiCk, SiCk, or combinations thereof; preferably the metal oxides are selected from the group comprising CeCk , ZnO, TiCk, SiCk; more preferably the metal oxide is Ce0 2 , b) dispersing metal-containing nanocrystal cores in an organic solvent under inert gas to provide a reaction mixture and maintaining the reaction mixture under inert gas atmosphere,
  • the one or more highly reactive organometallic compounds are able to produce volatile secondary products during the reaction and are preferably selected from the group comprising trimethyl aluminum, dimethylzinc, tetrakis(dimethylamido)titanium(IV), trymethylindium, trymethylgallium or combinations thereof, more preferably selected from the group comprising trimethyl aluminum, dimethylzinc, tetrakis(dimethylamido)titanium(IV), trymethylindium, or trymethylgallium, most preferably selected from the group comprising trimethyl aluminum, dimethylzinc, or tetrakis(dimethylamido)titanium(IV),
  • terminating ligands selected from the group comprising fatty acids, long chain amine and phosphine oxides, or combinations thereof, to the reaction mixture to stop the growth of the metal oxide shell, wherein preferably the fatty acids are selected from the group comprising oleic acid, myristic acid, stearic acid, or combinations thereof, and wherein preferably the long chain amine and phosphine oxides are selected from the group comprising dodecylamine, oleylamine, trioctylphosphine, trioctylphospineoxide, or combinations thereof.
  • the terminating ligand is oleic acid.
  • the method of the invention is conducted as a one-pot reaction, in which the metal-containing nanocrystal cores, the organic solvent, the inert gas, the one or more highly reactive organometallic compounds, the pure oxygen and the terminating ligands are added to a reactor to form the core-shell nanocrystals.
  • the organic solvent is selected from the group comprising saturated aliphatic hydrocarbons selected from the group comprising pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane; saturated alicyclic hydrocarbons selected from the group comprising cyclohexane and cycloheptane; and aromatic hydrocarbons selected from the group comprising toluene, xylene, trimethylbenzene, ethylbenzene, ethyltoluene, and indene.
  • the organic solvent is octane.
  • the inert gas is selected from the group comprising argon, nitrogen and helium.
  • the term“highly reactive organometallic compounds” refers to compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, such as alkaline, alkaline earth, and transition metals. These compounds are typically highly reactive due to the polarized metal-carbon bond and are able to produce volatile secondary products during the reaction.
  • the highly reactive organometallic compounds are in a liquid form.
  • the one or more highly reactive organometallic compounds is first diluted / dissolved in the organic solvent before introduction to the reaction mixture.
  • the organic solvent is selected from the group comprising saturated aliphatic hydrocarbons selected from the group comprising pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane; saturated alicyclic hydrocarbons selected from the group comprising cyclohexane and cycloheptane; and aromatic hydrocarbons selected from the group comprising toluene, xylene, trimethylbenzene, ethylbenzene, ethyltoluene, and indene.
  • the organic solvent is octane.
  • the one or more highly reactive organometallic compounds are selected from the group comprising trimethyl aluminium, dimethylzinc, tetrakis(dimethylamido)titanium(IV), trymethylindium, trymethylgallium or combinations thereof.
  • the one or more highly reactive organometallic compounds are selected from the group comprising trimethyl aluminium, dimethylzinc, tetrakis(dimethylamido)titanium(IV), or trymethylindium, trymethylgallium.
  • the one or more highly reactive organometallic compounds are selected from the group comprising trimethyl aluminium, dimethylzinc, or tetrakis(dimethylamido)titanium(IV).
  • the introducing one or more highly reactive organometallic compounds to the reaction mixture is done with an injection rate of from 0.5 to 1.5 ml/hour, preferably 1 ml/hour to avoid precipitation of the metal-containing nanocrystal cores.
  • the time in step d) necessary to allow deposition of the one or more highly reactive organometallic compounds on the surface of the metal-containing nanocrystal cores is at least 5 minutes and maximum 15 minutes.
  • the time is from 5 to 15 minutes, or 4 to 20 minutes, or 5 to 30 minutes.
  • the time in step f) necessary to obtain formation of a metal oxide layer on the surface of the metal containing nanocrystal cores and thereby growth of a metal oxide shell on the surface of the metal-containing nanocrystal cores is at least 5 minutes and maximum 15 minutes.
  • the time is from 5 to 15 minutes, or 4 to 20 minutes, or 5 to 30 minutes.
  • the optimal thickness of the metal oxide shell layer is from 1 nm to 20 nm; preferably 1 nm to 6 nm.
  • the core-shell nanocrystals of the invention can be used in a liquid form for coating of devices, surfaces or other applications where the liquid form is suitable. Thus no recovering is needed from the reaction mixture.
  • the advantage of the reagents/precursors used in the c-ALD method of the invention is that they are volatile and therefore no purification steps are needed. Indeed, the highly reactive organometallic compounds used in the present invention generate only methane or other volatile compounds after reaction and octane is also a volatile solvent.
  • the method of the invention further comprising recovering the core shell nanocrystals from the reaction mixture by precipitation or by evaporation of the solvent.
  • Another aspect of the invention provides core-shell nanocrystals consisting of a metal- containing nanocrystal core and a shell layer comprising at least one metal oxide material, obtained by the method of the invention.
  • the core-shell nanocrystal of the invention consists of a metal-containing nanocrystal core and a shell layer comprising at least one metal oxide material, wherein the metal-containing nanocrystal core is selected from the group comprising semiconductors, metals, metal oxides or combinations thereof,
  • the semiconductors are selected from the group comprising CdSe, ZnSe, InP, ZmP2, InSe, C-dot, CsPbX 3 (wherein X is Br, I, or Cl), or combinations thereof, preferably the semiconductors are selected from the group comprising CdSe, C-dot, CsPbX 3 (wherein X is Br, I, or Cl), wherein the metals are selected from the group comprising Ag, Au, Pt, Pd, or combinations thereof; preferably the metals are selected from the group comprising Ag, Au, Pt, Pd; more preferably the metal is Ag,
  • the metal oxides are selected from the group comprising CeC , ZnO, TiC , SiC , or combinations thereof; preferably the metal oxides are selected from the group comprising CeC , ZnO, TiCk, S1O2; more preferably the metal oxide is Ce0 2 , wherein the at least one metal oxide material is selected from the group comprising AI2O3 - X (where 0 ⁇ x ⁇ 3), TiCk- x (where 0 ⁇ x ⁇ 2), ZnOi- x (where 0 ⁇ x ⁇ l).
  • a thickness of the shell layer comprising the at least one metal oxide material is from 1 nm to 20 nm; preferably 1 nm to 6 nm.
  • the core-shell nanocrystals of the invention is a hybrid material platform wherein an oxide shell with tunable thickness allows to stabilize sensitive cores and to study both chemical transformations and electronic interactions occurring at the nanoscale.
  • the anion exchange reaction in the CsPbX 3 perovskites nanocrystals was performed by in situ X-ray diffraction, which had been impeded so far by the instability of this class of materials and by the fast exchange kinetics.
  • a careful distance-dependent studies on the transfer of excitonic energy in semiconductor NC films was demonstrated.
  • the core-shell NCs of the invention allows for example to observe energy transfer in a system where it was previously excluded, specifically between CsPbBr3 NCs and CdSe NPLs.
  • the optimal amount of trimethyl aluminium (TMA) diluted in octane is added drop-wise to nanocrystals (NCs) solution; after a sufficient reaction time (such as 5 minutes), O2 gas is introduced followed by other waiting time (such as 5 minutes). These steps constitute one cycle, which is then repeated multiple times to allow a layer-by-layer deposition of metal oxide (such as A10 x ). It was observed that after a certain number of cycles (typically 8-10 cycles) the as-synthesized core-shell nanocrystals (NCs) would lose their colloidal stability. In order to prevent this issue, when this stage is reached, OLAC is added in place of the O2 to prevent the formation of any precipitate.
  • NMA trimethyl aluminium
  • NC nanocrystal
  • Figure 3 gives an overview on the synthesized core-shell NCs with different compositions (i.e., CsPbBr 3 @A10 x , Ce0 2 @A10 x , Ag@A10 x NCs, where x is ⁇ 1.5) characterized by electron microscopy and DLS.
  • the HAADF-STEM images with the corresponding EDX maps in Figure 3A-E and the low magnification TEM images in Figure 4 evidence the preservation of the size and shape of the inorganic core which is surrounded by a lower density alumina shell whose thickness increases with the number of cycles (Figure 3E).
  • the results show a fine-tuning of the shell thickness ranging from 1 nm to 6 nm and an estimated growth rate during the c-ALD of around 0.36 nm/cycle.
  • the similarity between the measured A10 x growth rate and the estimated bond length suggests that each cycle correspond to the growth of a single layer around the NC core.
  • the TEM images in Figure 10 show that if no O2 is added during the c-ALD process the NCs start to aggregate upon addition of TMA and the final product is a precipitate containing aggregated NCs. If the TMA is added too quickly ( ⁇ 1 ml/h) or the waiting time between one- step and the other is too small ( ⁇ 5 min), the A10 x will growth separately from the NCs (see inset), resulting in a precipitate.
  • the Ag@A10 x NCs were chosen as the model system because of their robustness and versatile surface chemistry compared to the CsPbX 3 and the CeCk NCs.
  • the metallic nature of the Ag NCs allows to study the role of surface oxidation considering that Ag is relatively easy to oxidize.
  • Ag NCs functionalized with OLAC Ag-OLAC NCs were obtained by performing a mild ligand exchange.
  • Ag NCs with an oxidized surface were obtained by flowing pure O2 gas in the Ag-OLAM NC solution.
  • the UV-Vis absorption spectra (Figure 13) evidenced a slight red shift in the plasmon peak consistent with the formation of a thin oxide shell around the Ag-OLAM NCs.
  • Figure 11A compares the FTIR spectra on both Ag NCs and CsPbBr3 NCs before and after c- ALD. It is evident that the -CH- vibrational stretching of the native ligands on the NCs are still present after the c-ALD, confirming that they are not removed. Moreover new features appear in the region between 700 and 1700 cm 1 (evidenced in gray) that could be only assigned to the alumina matrix formed on the synthesized core-shell NCs. The peak at -800-900 cm 1 is assigned to the Al-0 absorbance phonon.
  • the method of the present invention is useful for coating sensitive nanocrystal cores, namely nanocrystal cores that are highly sensitive to polar environment (i.e. water or alcohols) such as perovskite nanocrystals.
  • polar environment i.e. water or alcohols
  • oxygen-rich groups such as diols or bi-carboxylic acids
  • the main advantages of the c-ALD method of the invention is that this is a solution-based method to grow a metal oxide shell with tunable thickness on the surface of nanocrystal core, where a highly reactive and cleanly decomposing precursor of the metal oxide is reacted directly with oxygen gas.
  • the method is carried out at room temperature and it is completed within a few hours.
  • the final core-shell nanocrystals stay soluble in solution (the core-shell nanocrystals are dispersed in the solution) or can be dried and used as powders, depending on the desired application.
  • the anion exchange reaction in the CsPbX 3 perovskites nanocrystals was studied by in-situ X-ray diffraction, a study impeded so far by the instability of these class of materials and by the fast exchange kinetics.
  • the advantage of the as-synthesized metal oxide shell, such as alumina shell was demonstrated by studying nanoscale chemical transformations by focusing on the anion exchange reaction in CsPbX 3 nanocrystals (NCs).
  • CsPbBr3 to CsPb(Br y Cli- y ) 3 or CsPb(Br y Ii- y )3) plays an important role in photostability, anomalous hysteresis and light induced segregation.
  • the ion diffusion mechanism in perovskite is still largely unknown. Because of the fast anion exchange kinetics (completed at the time scale of seconds), the few studies conducted so far have used optical probes, which provide only indirect proofs of structural changes.
  • the anion exchange reaction is slowed down by an order of magnitude and in-situ X-ray diffraction (XRD) studies could be performed.
  • XRD in-situ X-ray diffraction
  • CsPbX 3 NCs should mix rapidly and reproducibly to ensure a homogeneous environment during the reaction while allowing the X-rays to capture structural information.
  • These requirements were fulfilled by building a home-made set-up where two NC solutions of different composition react in a capillary (see Examples and Figure 15 for details).
  • the solution of the CsPbX 3 @A10 x NCs with different shell thicknesses and composition, all in anhydrous octane were simultaneously injected through a mixing frit placed at the entrance of the reaction chamber (i.e., the capillary) in which the two CsPbX 3 NCs have a few sub-milliseconds to mix.
  • This time is shorter than the time needed for the exchange to come to completion, which varies from seconds to tens of minutes depending on the investigated NCs (composition and w/o shell) as discussed later.
  • the structural changes occurring during the exchange were monitored in real time by acquiring XRD patterns every 2.5 s.
  • FIG 16A summarizes schematically the in-situ experiments that were performed.
  • CsPbBr3 @A10 X NCs with two different A10 x shell thickness constitute one of the reagents and they will be referred to as Br/no-shell, Br/shelll and Br/shell2, respectively.
  • CsPbCT NCs, CsPbE NCs and CsPbl 3 @A10 x shell 1 NCs were selected.
  • FIG. 18A A representative data set of the temporal evolution of the XRD patterns during the reaction from CsPbBr 3 @A10 x NCs to CsPb(Bro . 5lo . 5)3 NCs with various A10 x shell thicknesses is shown in Figure 18A.
  • the maps report the time evolution of the two reagents in a selected region of the XRD spectrum between 14.5 and 15.7 degrees which allows one to monitor the (211) diffraction peak from [CsPbBr 3 @A10 x NCs + CsPbl 3 @A10 x NCs] at time 0 to the final CsPb(Bro . 5lo . 5)3 composition.
  • the anion exchange study performed in this work exemplifies the new opportunities offered by nm-thick metal oxide shell around active NC cores.
  • the proposed systems could also act as materials platform to study solid-state ion diffusion across metal oxides, which is extremely interesting for perovskites solar cell, wherein an oxide layer acts both as electron or hole transporting layer to improve the charge transport and to reduce the instability issue due to diffusion of metal contact into the active perovskite layer.
  • the oxide shell could enable distance-dependent energy transfer studies between various donor and acceptor NCs (e.g. metal/semi conductor, semiconductor/semiconductor see Figures 21-25) as an alternative to using ligands of different lengths.
  • CsPbBr 3 NCs with a shell of titanium oxide and zinc oxide are shown in Figures 26-27;
  • CdSe nanoplates (NPLs) with a shell of zinc oxide and titanium oxide are shown in Figure 28;
  • carbon dots (C-Dots) with a shell of titanium oxide is shown in Figure 29.
  • Another aspect of the present invention provides a use of the core-shell nanocrystals of the invention as quantum dots or semiconductor nanocrystals.
  • QD-LED quantum dot light emitting diode
  • Quantum dot light emitting diodes are used for example for display and lighting sources. Inorganic quantum dot light emitters have a few advantages over OLEDs and other light-emitting diodes, which include stability, solution processability and excellent colour purity.
  • Quantum dots are semiconductor nanocrystallites whose radii are smaller than the bulk exciton Bohr radius. Quantum confinement of electrons and holes in all three dimensions leads to an increase in the effective band gap of the QDs with decreasing crystallite size, where the optical absorption and emission of quantum dots shift to higher energies (blue shift) as the size of the dots decreases.
  • a CdSe QD can emit light in any monochromatic visible color depending only on the size of the QD and can be used to form QD-LEDs arrays that emit white light.
  • Embodiments of the invention are directed to quantum dot light emitting diode (QD-LED) that include a light emitting layer having a plurality of quantum dots and an electron injection and transport layer having a plurality of inorganic nanoparticles, wherein the quantum dots are the core-shell nanocrystals of the invention, wherein preferably the core-shell nanocrystals of the invention are perovskite@A10x.
  • QD-LED quantum dot light emitting diode
  • Metal oxide core-shell nanocrystals can be used and implemented in many areas of science, including biology, health care and catalysis.
  • the core-shell nanocrystals of the invention can be used as electro-catalyst for example for CO2 reduction, oxygen and hydrogen evolution reactions.
  • Other catalytic applications are in thermal catalysis for various conversion reactions.
  • the core-shell nanocrystals of the invention have been used in bio applications such as controlled and targeted drug delivery, cell labelling and tissue engineering applications.
  • the core-shell nanocrystals of the invention are preferably metal@A10x.
  • Embodiments of the inventions are directed to catalytic and bio-devices that include at least one core-shell nanocrystals of the invention.
  • a catalytic material comprising at least one core-shell nanocrystals of the invention.
  • the catalytic material is selected from the group comprising electro-catalyst, photo-catalyst, thermal-catalyst.
  • a bio-material comprising at least one core-shell nanocrystals of the invention.
  • the bio-material is selected from the group comprising controlled and/or targeted drug delivery materials, cell labelling materials.
  • a photovoltaic device comprising at least one core-shell nanocrystals of the invention.
  • a light emitting material or device comprising at least one core-shell nanocrystals of the invention.
  • an ink or paint comprising at least one core-shell nanocrystals of the invention.
  • a display including at least one core-shell nanocrystals of the invention.
  • an electronic device including at least one core-shell nanocrystals of the invention.
  • Cs-oleate (Cs-OLA) precursor 0.8 g of CS2CO3, 2.5 mL OLAC and 80 mL ODE were added to a 100 mL 3 -necked round bottom flask and stirred under vacuum for lh at 120 °C. The flask was purged with N2 for 10 min and then placed back under vacuum. This process of alternately applying vacuum and N2 was repeated for a total of 3 times to remove moisture and O2. The reaction temperature was increased to 150°C and kept at this temperature until the solution was clear, indicating that the CS2CO3 has completely reacted with the OLAC. The Cs- OLA solution in ODE was stored in N2 until needed for the NC synthesis.
  • This Cs-OLA was used for the synthesis of CsPbBr3 and CsPbCb NCs. Instead for the synthesis of CsPbL NCs the amount of reagents was slightly different: 0.25 g of CS2CO3, 1 mL OLAC and 25 mL ODE, while the procedure was kept the same.
  • CsPbX 3 NCs synthesis were synthesized by following procedure.
  • PbBr2 (0.21 g) or PbCb (0.26 g) and ODE (15 mL) were stirred in a 50 mL round bottom flask and degassed under vacuum at 120 °C for 1 h. The flask was then filled with N2 and kept under constant N2 flow. OLAC and OLAM (1.5 mL each) were injected and the mixture was kept at this temperature until all the PbBr2 was dissolved. The temperature was then increased to 165 °C.
  • the Cs-OLA (1.2 mL) precursor pre-heated to 100 °C under N2 atmosphere, was swiftly injected into the reaction mixture.
  • the reaction mixture turned yellow or white and the reaction was quenched by immediate immersion of the flask into an ice bath ( ⁇ 5 s after injection).
  • the synthesized NCs were precipitated by centrifugation at 6000 rpm for 30 min, the supernatant was removed and the NCs were re dissolved in 1.5 ml of hexane.
  • a second wash was carried out by adding ethyl acetate in a ratio 1 : 1 with hexane, the mixture was centrifuged and the precipitate was dissolved in octane obtaining a final concentration of ⁇ 10 mg/ml.
  • CsPbL NCs The synthesis of CsPbL NCs was carried in the same way with some modification in the amount of reagent used: PbL (0.70 g), 35ml ODE, OLAC and OLAM 3.5 each and 5.6ml of Cs-OLA prepared as described previously was injected. Methyl acetate was used for the second washing. CeC NCs synthesis. CeC NCs were synthesized by following procedure. 1 mmol of Ce(N0 3 ) 3* 6H 2 0 was mixed with 1 mL of OLAM in 6.3 mL of ODE at room temperature and dissolved at 80°C for 30 min. Ce0 2 NCs were grown by heating the mixture at 260°C for 2h.
  • the as-prepared NCs were purified by washing, precipitation and centrifugation cycles, using ethanol, acetone and hexane at least 4 cycles to remove any unreacted cerium precursor, surfactants, and excess ODE.
  • the resultant dark brown precipitate was re-dispersed in octane in a concentration of around 10 mg/ml.
  • Ag NCs synthesis Ag NCs were synthesized by following procedure. 1 mmol AgNCb was mixed with 20 ml OLAM at room temperature followed by heating up to 60°C, which was maintained until the granular AgN0 3 crystals were completely dissolved. The solution was then quickly heated up (>10°C/min) to 180°C and the temperature was maintained for lhr before the reaction system was cooled down to room temperature. The resulting dark-brown solution was washed with acetone and re-dispersed in octane. Size-selective precipitation was used to narrow their size distribution.
  • Ag NCs with OLAC as ligand were obtained by using ligand stripping procedure. 1ml of acetonitrile containing Me0 3 BF 4 was added to 1ml of Ag NCs with native OLAM ligands (Ag-OLAM NCs) dispersed in hexane (with a concentration of 10 mg/ml by ICP-OES); after 1 min stirring, 1 ml of toluene was added and the mixture was centrifuged to allow NCs precipitation. The obtained NCs were dispersed in 1 ml DMF.
  • FIG. 1 sketches the synthesis set up.
  • One c-ALD cycle consists of: 1) drop-wise addition of TMA diluted in octane to the NC solution (the optimized rate of the syringe pump was fixed at lml/h); 2) 5 min waiting time so to ensure that the reaction in step 1) was completed; 3) addition of O2 gas by mean of a mass flow controller; 4) 5 min waiting time. This cycle is repeated n-times to reach the desired thickness.
  • the optimal amount of TMA 80 m ⁇ from a diluted TMA solution in octane with a concentration of 0.4* 10 3 mM
  • the optimal amount could slightly change from batch to batch.
  • the full process was automated by a home-made Lab- View software where precursor amount, injection speed, and waiting time are independently defined. Different c-ALD conditions were tested to optimize the process ( Figure 10).
  • OLAC was introduced in place of TMA after 8-10 cycles.
  • This step functionalizes the surface of the shell which can continue to grow without any precipitation of the NCs.
  • a gas tight syringe was used for the TMA injection to ensure that the TMA concentration stayed unchanged during the full process.
  • the TMA is used in very diluted amount to avoid any safety issue.
  • the reaction mixture turned yellow, and the reaction was quenched by immediate immersion of the flask into an ice bath ( ⁇ 5 s after injection).
  • the synthesized NCs were precipitated by centrifugation at 6000 rpm for 30 min, the supernatant was removed, and the NCs were re-dissolved in 1.5 mL of hexane.
  • a second wash was carried out by adding ethyl acetate in a 1 : 1 ratio with hexane, the mixture was centrifuged, and the precipitate was dissolved in octane, giving a final concentration of ⁇ 10 mg/mL.
  • CdSe NPLs synthesis Cd(myristate)2 was synthesized according to reported procedure. 22 170 mg of Cd(myristate)2 and 14 ml of ODE were degassed for 30min at room temperature in a three neck-flask. Then under N2 the flask was heated to 240°C. Meanwhile, 12 mg of Se powder was sonicated in 1ml ODE for 5min. At 240°C the Se solution was quickly injected in the reaction mixture and after 20 seconds (the solution became dark orange), 60mg of Cd(Ac)2 was introduced. The reaction mixture was kept at 240°C for 10 min and then was cooled down with to 150°C with air-flow, and allowed to slowly cool down further.
  • One c-ALD cycle consists of (1) dropwise addition (1 mL/h) of trimethyl aluminium (TMA) diluted in octane to the NC solution; (2) 5 min waiting time to ensure that the reaction in step 1 was completed; (3) addition of O2 gas by mean of a mass flow controller; and (4) 5 min waiting time.
  • This cycle is repeated n times to reach the desired thickness. 80 pL from a diluted TMA solution in octane with a concentration of 0.4x l0 -3 pM were added each cycle. Some minimal adjustement might be needed from batch to batch. The full process was automated by using a custom-made Lab-View program where precursor amount, injection speed, and waiting time are independently defined.
  • OLAC was introduced in place of TMA after 8-10 cycles. This step functionalizes the surface of the shell, which can continue to grow without any precipitation of the NCs.
  • CsPbBr 3 @A10 x NCs with different shell thickness were synthesized ranging from 1.5 to 10 nm thick.
  • Electron Microscopy Transmission electron microscopy (TEM) images were acquired on a FEI Tecnai-Spirit at 120 kV. High-angle annular dark-field scanning TEM (HAADF-STEM) images and X-ray energy dispersive (EDX) elemental maps were acquired on a FEI Tecnai-Osiris at 200 kV. This microscope is equipped with a high brightness X-FEG gun, silicon drift Super-X EDX detectors and a Bruker Esprit acquisition software. Samples were prepared by dropping hexane or octane solution containing the nanoparticles on the surface of ultrathin carbon-coated copper grids (Ted Pella, Inc.).
  • Optical Spectroscopy All optical measurements including photoluminescence (PL) emission spectra, time-resolved fluorescence lifetimes (TRPL) and quantum yield (QY) measurements were collected on a Horiba Jobin Yvon Fluorolog-3 with a PMT as detector.
  • the crude CsPbX 3 NC solutions were diluted in octane to reach an optical density of about 0.1-0.2 at the excitation wavelength.
  • the excitation source is a Horiba nanoLED-370 with an excitation wavelength of 369 nm, a pulse duration of 1.3 ns and a repetition rate of 100 kHz.
  • the absolute QY measurements were performed in the integrating sphere Fluorolog-3 accessory where a quartz cuvette containing the sample was placed. The sample was excited with a monochromated xenon lamp at 470 nm. The emitted light was collected at the exit of the sphere by a PMT detector.
  • UV-vis absorption measurements were performed in transmission mode using a PerkinElmer Lambda 950 spectrophotometer equipped with a deuterium lamp as a light source for the ultraviolet range and a tungsten halide lamp as a light source for the visible and infrared range, and a PMT with a Peltier-controlled PbS detector.
  • DLS measurements were carried out using a Zetasizer Nano ZS (Malvern) instrument.
  • the Nano ZS system is equipped with a 4 mW red laser (633 nm) and a detection angle of 173°.
  • the samples were prepared in a quartz cuvette in octane solvent. For each sample 3 measurements were performed with a fixed run time of 10s.
  • the Malvern DTS 5.10 software was applied to process and analyze the data.
  • Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR).
  • ATR-FTIR was performed using a Perkin Elmer instrument Spectrum 100 by drop-casting 30 m ⁇ of the NC solution on the ATR window, and measured with a resolution of 4 cm 1 .
  • ICP-OES Inductively Coupled Plasma - Optical Emission Spectrometry
  • the raw data were processed into powder patterns with Bubble. To monitor the evolution of the lattice parameters, all patterns were fitted using the Le Bail method.
  • the utilized crystallographic data were taken from the ICSD database: CsPbBr3 (Pm-3m, collection code: 97852), CsPbL (Pm-3m, collection code: 161481), and CsPbCh (Pm-3m, collection code: 29067).
  • metal oxide such as AlOx
  • A10 x shell thickness was determined by grazing incident small angle X-ray scattering (GISAXS) and Dynamic Light Scattering (DLS) measurements.
  • GISAXS measurements were performed at the ID10-EH1 beamline at the ESRF - European synchrotron in Grenoble.
  • the X-Ray energy was set to 22 KeV (0.56356 A) and the distance between the sample and the detector was fixed at 4284.5 mm.
  • the beam size was 35 pm tall by 13 pm wide at the sample position.
  • the grazing-incident angle of the X- ray beam was 0.078°.
  • 2D scattering data were collected by using a Maxipix 2x2 (CdTe) - EH2 detector which was calibrated using a Ag-Behenate standard.
  • CsPbBr 3 @A10 x NCs with different shell thickness were deposited on lxl cm 2 silicon substrates. The inter-particle distance between the NCs was extracted by integrating the 2D maps at azimuthal angle by using Fit2D software.
  • DLS measurements were carried out using a Zetasizer Nano ZS (Malvern) instrument.
  • the Nano ZS system is equipped with a 4 mW red laser (633 nm) and a detection angle of 173°.
  • the samples were prepared in a quartz cuvette in octane solvent. For each sample, three measurements were performed with a fixed run time of 10 s.
  • the Malvern DTS 5.10 software was applied to process and analyse the data.

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Abstract

La présente invention concerne un procédé de production de nanocristaux cœur-écorce constitués d'un cœur nanocristallin contenant du métal et d'une couche d'écorce comprenant au moins un matériau d'oxyde métallique ayant des épaisseurs d'écorce variables, et l'utilisation des nanocristaux coeur-écorce pour différentes applications.
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